Such a vacuum cleaner is known from EP-A-0121511.
It is known that dust can be effectively removed from an air flow by a cyclone filter system. A cyclone filter system, however, has the disadvantage that the material separated by the cyclone in the collector reservoir is subjected to small forces so that little densification takes place there in the case of fluffy material. As a result, the filling of the reservoir, also when the latter is full, consists mainly of air.
A normal paper dust bag of a comparable volume can contain a much greater mass of dust. This is because the material collected is continuously pressed home by the air sucked through it, so that the material is densified. A further advantage of a paper dust bag is that it can be easily and hygienically removed and disposed with. A disadvantage of a paper dust bag, however, is that fine dust quickly chokes up the bag, so that the flow resistance increases markedly and the air flow is strongly reduced. In addition, it is not ideal always to be dependent on a comparatively expensive paper dust bag which has to be re-purchased every time.
In EP-A-0121511 cited above the advantages of both filter systems are combined. For a cyclone this is the property that the flow resistance is independent of the quantity of dust already separated, and for the filter system the property that the separated dust is densified.
The vacuum cleaner described in EP-A-0121511 is a street vacuum cleaning machine. This machine comprises a separate collector reservoir for the dust from each of the filter systems. Both reservoirs are to be emptied from time to time. In view of the kind of refuse which is sucked up, the use of two reservoirs would seem to be necessary. If such a dual filter system should be used in a household vacuum cleaner, however, two collector reservoirs are inconvenient to use.